Edward R. Cozzi

Don't forget the #5 SSM was Mercruisers answer to the Kiekhaefer #6 before the companies merged.
I believe the #5 gets more power to the prop. Those massive shafts and gears in the #6 are strong, but it takes more power to turn them.
Correct me, but aren't the #5s much less expensive?

Falcon

The dry#6 put's more power to the water than the #5, but the other arguments "may" be true depending on the application. If you put standoff boxes on the 5's and external steering, the weights are not really that far apart. If you can run a high x dimension, the drag issues are not far apart either. Also add in the cost of the standoff boxes and steering cylinders when considering overall cost. It's still probably less costly to put on 5's, just pointing out the other things to consider.

RMPRam

I've have an old (1984) 38 Cigarette flat deck with a kevlar hull. The boat came orig. with a pair of 540 Hawks and #3 SSM drives. I now have a pr. of 572 PSI supercharged motors using #5 drives and Stellings box's. It now runs 104-105.
I thought about using #6's, before I bought the #5's, and went with the 5's for the cost and I was also told that the boat would be slower with #6's. I'm not sorry that I used the 5's as I have not had any trouble with running 1100hp. motors through them with a 1.48 ratio and 17.5x31 4 bbl. props. With no spacers in the drives, the prop shaft is 1/2" above the bottom of the boat.
I've tried spacers from 1",2" and 3" and they don't seem to make any difference other than it is a lot easier to get on plane with the 3" installed.
I noticed that you were running 5 bbl. props. Have you tried others? Have you tried spacers?
Keep in mind that if you switch to #6s and don't run driveline transmissions, the tailstocks for a plug-in #6 are approx. $2500 ea. and that does not include the transmission. Factor that into your decision.
If I can be of any assistance, I would be happy to.

Jassman

It sounds like alot of trial and error. I to am running either a 1.47 or 1.48 ratio. The spacers if they didnt hinder performance on top end but helped getting on plane might be the anwser. Just wondering if boxes help or hurt. Nortech did a beautiful job prefabing a few pieces to make everything work for what I gave them. Looks like Im going to have a little paint work once I pull them off. Jeff

Question: is it better to pull boxes off first or just try spacers, thanks Jeff

RMPRam

If you decide to try spacers, you will need the stud kit for the thickness of spacer that you choose. You can use a 1" or a 2" or you can combine them both to make a 3". I've never seen anything thicker used, as I think you run out of internal splines at that point.
I have a set of 1" spacers, that I had machined from alum., that I added a 9" "tail" to act as a cavitation plate, that helped in getting the boat on plane. If you are interested I would sell them for $500.
Gary @ 763-473-8963 eves/weekends

Jassman

Do you by chance have a picture of what you are talking about, thanks Jeff

10x

Jassman..... Before you do anything, check the height of the prop shaft in relation to the bottom of the boat. What I mean is, with the prop shafts perfectly parralell with the bottom of the boat, run a straight edge down the bottom in line with the drive.
Generally speaking, with boxes, and this will differ from boat to boat, your prop shafts should be somewhere within 1" of the bottom. The deeper you go, as with the spacers, usually the more drag you will have therefor slowing you down a bit.
On the other hand, the higher you go will make it harder to get on plane, but let you run faster on the top.
You need to find the "happy medium" then prop it accordingly.

RMPRam

Call me and lets talk.
Gary @ 763-473-8963

mcollinstn

wet sixes eat a few more horses on the way to the prop (than a 5)
dry sixes eat a few less horses on the way to the prop (than a 5)

six gearcase has atouch more drag than a 5 gearcase.

high x dims negate that difference (when running w/centerline above bottom of hull)

My guess is that if you already have fives installed, that there would be questionable benefit in swapping to dry sixes for the cost and hassle involved. There would be no benefit in swapping to wet sixes.

Jassman

I had my wife give me a hand, to get it as accurate as possible. I have a notch in my transom so at that measurement the props are approx 6 1/2"-7" above the bottom of the notch. (very bottom of boat)

At the other bottom of the boat, above the notch it is almost dead nuts, about a 1/2" -1"above . Any more help is apprieciated. Jeff